Photosensitive composition and use thereof

ABSTRACT

A photosensitive composition containing a curable cyanate ester and a cationic photoinitiator; and use thereof to form a resist image.

This application is a division of Ser. No. 07/283,311, filed on Jul. 20,1989, now abandoned.

TECHNICAL FIELD

The present invention is concerned with photosensitive compositions andparticularly with photosensitive compositions that can act as positiveor negative resists, depending upon the type of photoinitiator employed.

Moreover, the present invention is especially concerned withcationically initiated photosensitive compositions which arethermosetting.

In addition, the present invention is directed to the production ofresist images employing the photosensitive compositions.

BACKGROUND ART

One widely used method for forming a pattern such as metallic circuitryon a substrate in the manufacture of printed circuit boards inintegrated circuits is to imagewise form a pattern of photoresistmaterial over those areas of the substrate or over a metal-coatedsubstrate to be shielded from metal deposition or metal removal. Thephotoresist layer is normally formed of a polymeric, organic materialthat is substantially unaffected by the metal deposition or metalremoval process and, accordingly, protects the underlying areas.

The pattern is formed by imagewise exposing the photoresist material toactinic light through a photographic image, such as a glass master, byphotolithographic techniques. The actinic light employed is usuallyX-ray, U.V. radiation, or electron beam radiation.

A number of photoresist materials are well-known and are capable offorming desired masking pattern. However, providing compositions whichexhibit acceptable imaging (resolution and acuity) characteristics to besuitable as an image or pattern mask, especially for integratedcircuits, along with the ability to tailor the composition to providingeither a positive or negative resist, is quite unusual.

Also, providing such compositions with the ability to achieve apermanent protective coating is even that much more difficult.

In the manufacture of printed circuit boards and cards it is desirablethat the photosensitive material used be patternable by means ofphotolytic process as is the practice with photoresists and which also,unlike most photoresists, can be retained to perform one or moreadditional functional uses during or after fabrication of the circuitboard.

SUMMARY OF THE INVENTION

It has been found, according to the present invention, that cyanateesters can be rendered photosensitive by mixing with a cationicphotoinitiator. It has also been found, according to the presentinvention, that photosensitive compositions containing cyanate estersare capable of performing such functions as permanently retained etchmask, solder mask, plating mask, dielectric film, and protectivecoating.

In particular, it has been found that photo-processable coatings of thepresent invention not only exhibit good resolution (e.g., sharplydefined acuity), but also possess excellent mechanical properties andespecially high temperature resistance, making such available use as asolder mask. Such are capable of withstanding the temperaturesexperienced (e.g., about 360° C.) when joining an integrated circuitchip(s) to a card or board by soldering.

In addition, the present invention makes it possible to provide positiveor negative resist, depending upon the type of photoinitiator selected.

In particular, the present invention is concerned with photosensitivecomposition that contains a curable cyanate ester and a cationicphotoinitiator.

In addition, the present invention is concerned with a method for theproduction of a resist image which includes providing on a substrate aphotosensitive composition. The photosensitive composition contains acurable cyanate ester and a cationic photoinitiator. The composition isimagewise exposed in a predetermined pattern to actinic light anddeveloped to thereby provide the resist image.

BEST AND VARIOUS MODES FOR CARRYING OUT THE INVENTION

The cyanate esters employed pursuant to the present invention have twoor more --O--C.tbd.N groups and are curable through cyclization ascontrasted to free radical curable materials that contain ethylenic oracetylenic unsaturation. Accordingly, the cyanate esters employed in thepresent invention are free from ethylenic and acetylenic unsaturation.

The cyanate esters can be monomeric or preferably polymeric, includingoligomers and can be represented by those materials containing thefollowing group: ##STR1## wherein A represents independently a simplebond, --S--, --S--S--, --SO--, --SO₂ --, --CO--, --CO₂ --, --O--,--C(CF₃)₂ --, divalent alkylene radicals such as --CH₂ -- and --C(CH₃)₂--; divalent alkylene radicals substituted with heteroatom such as O, S,and N; divalent alkylene radicals interrupted by heteroatoms in thechain such as O, S, and N; divalent cyclicalkylene groups and divalentarylene groups.

Each R is independently selected from the group of hydrogen, alkylcontaining 1 to 9 carbon atoms, aryl containing 6 to 14 carbon atoms,alkaryl containing 6 to 14 carbon atoms, and halogen.

Each n independently is an integer of 0 to 4.

Specific cyanate esters that can be employed in the present inventionare available and well-known and include those discussed in U.S. Pat.Nos. 4,195,132; 3,681,292; 4,740,584; 4,745,215; 4,477,629; and4,546,131; European patent application EP0147548/82; and German Offen.2611796, disclosures of which are incorporated herein by reference. Someexamples of suitable cyanate esters are 4,4'-dicyanatodiphenyl,2,2'-dicyanatodiphenyl, 3,3',5,5'-tetramethyl-4,4'-dicyanatodiphenyl,3,3',5,5'-tetrachloro-4,4'-dicyanatodiphenyl,3,3',5,5'-tetrachloro-2,2'-dicyanatodiphenyl,2,2',6,6'-tetrachloro-4,4'-dicyanatodiphenyl,4,4'-bis-[(3-cyanato)-phenoxy]diphenyl,4,4'-bis-[(4-cyanato)-phenoxy]-diphenyl; 2,2'-dicyanato-1,1'-binaphthyl;4,4'-dicyanatodiphenyl ether,3,3',5,5'-tetramethyl-4,4'-dicyanatodiphenyl ether,3,3',5,5'-tetrachloro-4,4'-dicyanatodiphenyl ether,4,4'-bis-[p-cyanatophenoxy]-diphenyl ether,4,4'-bis-[p-cyanatophenylisopropyl]-diphenyl ether,4,4'-bis-[p-cyanatophenoxy]-benzene, 4,4'-bis-[m-cyanatophenoxy]diphenylether, 4,4'-bis-[4-(4-cyanatophenoxy)-phenyl sulphone]-diphenyl ether;4,4'-dicyanatodiphenyl sulphone,3,3',5,5'-tetramethyl-4,4'-dicyanatodiphenyl sulphone,3,3',5,5'-tetrachloro-4,4'-dicyanatodiphenyl sulphone,4,4'-bis-[p-cyanatophenylisopropyl]-diphenyl sulphone,4,4'-bis-[(4-cyanato)-phenoxy]-diphenyl sulphone,4,4'-bis-[(3-cyanato)-phenoxy]-diphenyl sulphone,4,4'-bis-[4-(4-cyanatophenylisopropyl)phenoxy]-diphenyl sulphone,4,4'-bis-[4-cyanatophenyl sulphone)-phenoxy]-diphenyl sulphone,4,4'-bis-[4-(4-cyanato)-diphenoxy] -diphenylsulphone;4,4'-dicyanatodiphenyl sulfide, 4,4'-dicyanatodiphenyl methane,4,4'-bis-[p-cyanatophenyl]-diphenyl methane,2,2-bis-(p-cyanatophenyl)-propane,2,2-bis-(3,5-dimethyl-4-cyanatophenyl)-propane,2,2-bis-(3,5-dichloro-4-cyanatophenyl)-propane,1,1-bis-[p-cyanatophenyl]-cyclohexane,bis-[2-cyanato-1-naphthyl]methane,1,2-bis-[p-cyanatophenyl]-1,1,2,2-tetramethyl ethane,4,4'-dicyanatobenzophenone, 4,4'-bis(4-cyanato)phenoxybenzophenone,1,4-bis-[p-cyanatophenylisopropyl]benzene,2,2',5,5'-tetracyanatodiphenyl sulphone; 2,2-bis (p-cyanatophenyl)hexafluoropropane; polycyanic acid esters of novolacs (reaction productsof phenol or alkyl- or halogen-substituted phenols with formaldehyde inacid solution) having from 3 to 5 OCN groups. Preferably, prepolymersincluding oligomers are employed as the cyanate esters. An example of asuitable polyaromatic cyanate ester containing cycloaliphatic bridginggroup between aromatic rings is available from Dow Chemical Companyunder the designation "Dow XU-71787.OOL cyanate. A discussion of suchcan be found in Bogan, et al., "Unique Polyaromatic Cyanate Ester forLow Dielectric Printed Circuit Boards", Sampe Journal, Vol. 24, No. 6,Nov/Dec 1988.

The compositions of the present invention also contain a photoinitiatorand especially cationic initiators. In the event a positive workingphotoresist composition is desired, the photoinitiator employed is onewhich will generate a Bransted acid upon exposure to actinic light.Examples of such photoinitiators are well-known and include onium saltsand especially Group VIA and Group VIIA salts such as the pyrylium,selenonium, sulfonium, and iodonium salts. Various suitablephotoinitiators are discussed in U.S. Pat. Nos. 4,161,478; 4,442,197;4,139,655; 4,400,541; 4,197,174; 4,173,476; and 4,299,938; and Europeanpatent application 44/0094914 and 84/0126712, disclosures of which areincorporated herein by reference.

Also see Watt, et al., "A Novel Photoinitiator of CationicPolymerization: Preparation and Characterization ofBis[4-(diphenylsulfonio)phenyl]-sulfide-Bis-Hexafluorophosphate",Journal of Polymer Science: Polymer Chemistry Edition, Vol. 22, p. 1789,1980 John Wiley & Sons, Inc.

Additional discussions concerning sulfonium and iodonium salts can befound, for instance, in Crivello, et al., "Complex Triarylsulfonium SaltPhotoinitiators. II. The Preparation of Several New ComplexTriarylsulfonium Salts and the Influence of Their Structure inPhotoinitiated Cationic Polymerization", Journal of Polymer Science:Polymer Chemistry Edition, Vol. 18, pp. 2697-2714 (1980), John Wiley &Sons, Inc.; Pappas, et al., "Photoinitiation of Cationic Polymerization.III. Photosensitization of Diphenyliodonium and TriphenylsulfoniumSalts", Journal of Polymer Science: Polymer Chemistry Edition, Vol. 22,pp. 77-84, (1984), John Wiley & Sons, Inc.; Crivello, et al.,"Photoinitiated Cationic Polymerization with Triarylsulfonium Salts",Journal of Polymer Science: Polymer Chemistry Edition, Vol 17, pp.977-999, (1979), John Wiley & Sons, Inc.; Crivello, et al., "ComplexTriarylsulfonium Salt Photoinitiators. I. The Identification,Characterization, and Syntheses of a New Class of Triarylsulfonium SaltPhotoinitiators", Journal of Polymer Science: Polymer Chemistry Edition,Vol. 18, pp. 2677-2695, (1980), John Wiley & Sons, Inc.; and Crivello,"Cationic Polymerization--Iodonium and Sulfonium Salt Photoinitiators",Advances in Polymer Science, Series #62, pp. 1-48 (1984),Springer-Verlag.

Examples of some sulfonium salts are arylacyldialkyl andhydroxyaryldialkyl sulfonium salts represented by the followingformulae: ##STR2## where R is a C.sub.(6-13) monovalent aromatic organicradical or substituted C.sub.(6-13) monovalent aromatic organic radical;R¹ is a monovalent radical selected from hydrogen, C.sub.(1-8) alkyl andmixtures thereof; R² is a C.sub.(1-13) monovalent organic radical; R³ isa monovalent radical selected from C.sub.(1-8) alkyl, hydroxy,C.sub.(1-8) alkoxy, halo and nitro; R⁴ is a C.sub.(1-8) alkyl radical; Mis a metal or metalloid; Q is halogen; and d is equal to 4-6.

Examples of arylacyldialkyl sulfonium salts are: ##STR3##

Examples of some hydroxyaryl dialkyl sulfonium salts are: ##STR4##

Other suitable photoinitiators are: ##STR5##

When a negative working photoresist is desired, the photoinitiatoremployed is one which will generate a Lewis acid upon exposure toactinic light. Examples of such photoinitiators are well-known andinclude iron arenes. Various suitable photoinitiators are discussed inMeier, et al., "Photoinitiated Cationic Polymerization of Epoxides withIron-Arene Complexes", Journal of Radiation Curing, October 1986, pp.26-32; Meier, et al., "Imaging with Iron Arene Photoinitiators" Journalof Imaging Science, Vol 30, No. 4, July/August 1986, pp. 174-177;Zweifel, et al., "Imaging with Cationic Organometallic Photoinitiators",Polymer Preprint, Vol. 26(2), 1985, pp. 347-348; and Meier,"Photopolymerization of Epoxides--A New Class of Photoinitiators Basedon Cationic Iron Arene Complexes", Society of Manufacturing Engineers,Technical Paper FC-85-417, 1985, disclosures of which are incorporatedherein by reference. Examples of some iron arene photoinitiators arerepresented by the formula: ##STR6## wherein L is an aryl group such asphenyl, naphthyl, and anthracyl; and X is a non-nucleophilic anion suchas SbF₆ ⁻, PF₆ ⁻, AsF₆ ⁻, BF₄ ⁻, CF₃ SO₃ ⁻, or ClO₄ ⁻. Such iron arenesare available including Ciba-Geigy CG-061 and RD-356.

The photoinitiator employed is present in an amount sufficient to eitherretard or initiate the polymerization of the cyanate ester, dependingupon the type of photoinitiator employed. Usually, the amount ofphotoinitiator is about 0.5% to about 10% by weight and preferably about3% to about 5% by weight based upon the solid resin weight.

If desired, the composition can also include a free radical initiator,such as a peroxide including cumyl peroxide, to increase the speed ofthe photoinitiation. It is believed that free radicals facilitate thedecomposition of iron arenes generating acid. When employed, such isusually present in amounts up to about 5% and preferably about 0,005% toabout 3% by weight of the solid resin weight.

If desired, in the case of negative photoresists, the compositions canalso include catalysts to promote the polymerization of the cyanateester. Such catalysts include Lewis acids, such as aluminum chloride,boron trifluoride, ferric chloride, titanium chloride, and zincchloride; salts of weak acids, such as sodium acetate, sodium cyanide,sodium cyanate, potassium thiocyanate, sodium bicarbonate, and sodiumboronate. Preferred catalysts are metal carboxylates and metal chelates,such as cobalt, iron, zinc, and copper actylacetonate or octoates ornaphthenates. The amount of catalyst used can vary, and generally willbe 0.005 to 5 weight percent, preferably 0.05 to 0.5 weight percentbased on total solid resin weight.

Furthermore, if desired, the composition can include one or morephotosensitizers. Suitable photosensitizers includeperylene(peri-dinaphthalene), anthracene derivatives (ex.9-methylanthracene), dyes (e.g., acridine orange, acridine yellow,benzoflavin), and titanium dioxide.

When employed, the photosensitizer is usually present in amounts of upto about 3% by weight and preferably about 0.1% to about 1.5% by weightbased upon the total solids weight content of the composition.

In addition, the cyanate esters can be blended with organic monomers orpolymers including oligomers. The polymers can be thermoplastic orthermosetting. Examples of organic modifiers are epoxies, allylesters,acetylene terminated resins, multifunctional maleimide resins, phenols,monofunctional or multifunctional, polyols, polyetherimides, polyimides,siloxane polyimides, fluorine containing polyimides, polyesters,polyacrylates, polysulfones, polyethersulfones, polycarbonates,polyestercarbonates, and acrylonitrile-butadiene-styrene polymers.

Examples of suitable epoxides containing oxirane ring that can beemployed are well-known and are described in E. W. Flick, "Epoxy Resin,Curing Agents, Compounds, and Modifiers" Noyes Publications, Park Ridge,N.J. (1987); in Lee and Nevill, "Epoxy Resins" McGraw-Hill, (1967); andin U.S. Pat. No. 4,680,341.

Typical examples of epoxy polymers include the epoxidized novolacpolymers and the polyepoxides from halo-epoxy alkanes such asepichlorohydrin and a polynuclear dihydric phenol such as bisphenol A.Mixtures of epoxides can be used when desired.

The epoxidized novolac polymers are commercially available and can beprepared by known methods by the reaction of an uncross-linked phenolicaldehyde of a phenol with a halo-epoxy alkane. The phenol can be amononuclear or polynuclear phenol. Examples of mononuclear phenols havethe formula: ##STR7## wherein X, Y, and R₅ are hydrocarbons containingno more than about 12 carbon atoms.

Hydrocarbon-substituted phenols having two available positions ortho orpara to a phenolic hydroxy group for aldehyde condensation to providepolymers suitable for the preparation of epoxy novolacs include o- andp-cresols, o- and p-ethyl phenols, o- and p-isopropyl phenols, o- andp-tert-butyl phenols, o- and p-secbutyl phenols, o- and p-amyl phenols,o- and p-octyl phenols, o- and p-nonyl phenols, 2,5-xylenol,3,4-xylenol, 2,5-diethyl phenol, 3,4-diethyl xylenol, 2,5-diisopropylphenol, 4-methyl resorcinol, 4-ethyl resorcinol, 4-isopropyl resorcinol,4-tert-butyl resorcinol, o- and p-benzyl phenol, o- and p-phenethylphenols, o- and p-phenyl phenols, o- and p-tolyl phenols, o- and p-xylylphenols, o- and p-cyclohexyl phenols, o- and p-cyclopentyl phenols,4-phenethyl resorcinol, 4-tolyl resorcinol, and 4-cyclohexyl resorcinol.

Various chloro-substituted phenols which can also be used in thepreparation of phenol-aldehyde resins suitable for the preparation ofthe epoxy novolacs include o- and p-chloro-phenols, 2,5-dichloro-phenol,2,3-dichloro-phenol, 3,4-dichloro-phenol, 2-chloro-3-methyl-phenol2-chloro-5-methyl-phenol, 3-chloro-2-methyl-phenol,5-chloro-2-methyl-phenol, 3-chloro-4-methyl-phenol,4-chloro-3-methyl-phenol, 4-chloro-3-ethyl-phenol,4-chloro-3-isopropyl-phenol, 3-chloro-4-phenyl-phenol,3-chloro-4-chloro-phenyl-phenol, 3,5-dichloro-4-methyl-phenol,3,5-dichloro-5-methyl-phenol, 3,5-dichloro-2-methyl-phenol,2,3-dichloro-5-methyl-phenol, 2,5-dichloro-3-methyl-phenol,3-chloro-4,5-dimethyl-phenol, 4-chloro-3,4-dimethyl-phenol,2-chloro-3,5-dimethyl-phenol, 5-chloro-2,3-dimethyl-phenol,5-chloro-3,5-dimethyl-phenol, 2,3,5-trichloro-phenol,3,4,5-trichloro-phenol, 4-chloro-resorcinol, 4,5-dichloro-resorcinol,4-chloro-5-methyl-resorcinol, 5-chloro-4-methyl-resorcinol.

Typical phenols which have more than two positions ortho or para to aphenolic hydroxy group available for aldehyde condensation and which, bycontrolled aldehyde condensation, can also be used are: phenol,m-cresol, 3,5-xylenol, m-ethyl and m-isopropyl phenols, m,m'-diethyl anddiisopropyl phenols, m-butyl-phenols, m-amyl phenols, m-octyl phenols,m-nonyl phenols, resorcinol, 5-methyl-resorcinol, 5-ethyl resorcinol.

Examples of polynuclear dihydric phenols are those having the formula:##STR8## wherein Ar is an aromatic divalent hydrocarbon such asnaphthylene and, preferably, phenylene; A and A₁ which can be the sameor different are alkyl radicals, preferably having from 1 to 4 carbonatoms, halogen atoms, i.e., fluorine, chlorine, bromine, and iodine, oralkoxy radicals, preferably having from 1 to 4 carbon atoms; x and y areintegers having a value 0 to a maximum value corresponding to the numberof hydrogen atoms on the aromatic radical (Ar) which can be replaced bysubstituents and R₆ is a bond between adjacent carbon atoms as indihydroxydiphenyl or is a divalent radical including, for example:##STR9## and divalent hydrocarbon radicals, such as alkylene,alkylidene, cycloaliphatic, e.g. , cycloalkylene and cycloalkylidene,halogenated, alkoxy or aryloxy substituted alkylene, alkylidene andcycloaliphatic radicals, as well as alkarylene and aromatic radicalsincluding halogenated, alkyl, alkoxy or aryloxy substituted aromaticradicals and a ring fused to an Ar group; or R¹ can be polyalkoxy, orpolysiloxy, or two or more alkylidene radicals separated by an aromaticring, a tertiary amino group, an ether linkage, a carbonyl group or asulfur containing group such as sulfoxide, and the like.

Examples of specific dihydric polynuclear phenols include, among others,the bis-(hydroxyphenyl)alkanes such as2,2'-bis-(4-hydroxyphenyl)propane, 2,4'-dihydroxydiphenylmethane,bis-(2-hydroxyphenyl)methane, bis-(4-hydroxyphenyl)methane,bis(4-hydroxy-2,6-dimethyl-3-methoxyphenyl)methane,1,1'-bis-(4-hydroxyphenyl)ethane, 1,2'-bis-(4-hydroxyphenyl)ethane,1,1'-bis-(4-hydroxy-2-chlorphenyl)ethane,1,1'-bis(3-methyl-4-hydroxyphenyl) ethane,1,3'-bis-(3-methyl-4-hydroxyphenyl)propane,2,2'-bis-(3-phenyl-4-hydroxyphenyl)propane,2,2'-bis-(3-isopropyl-4-hydroxyphenyl)propane,2,2'-bis(2-isopropyl-4-hydroxyphenyl)pentane, 2,2'-bis-(4-hydroxyphenyl)heptane, bis-(4-hydroxyphenyl)phenylmethane,bis-(4-hydroxyphenyl)cyclohexylmethane,1,2'-bis-(4-hydroxy-phenyl)-1,2'-bis-(phenyl)propane and2,2'-bis-(4-hydroxyphenyl)-1-phenyl-propane; di(hydroxyphenyl) sulfonessuch as bis-(4-hydroxyphenyl)sulfone, 2,4'-dihydroxydiphenylsulfone,5'-chloro-2,4'-dihydroxydiphenyl sulfone, and5'-chloro-4,4'-dihydroxydiphenyl sulfone; di(hydroxyphenyl)ethers suchas bis-(4-hydroxyphenyl)ether, the 4,4'-, 4,2'-, 2,2'-, 2,3'-,dihydroxydiphenyl ethers, 4,4'-dihydroxy-2,6-dimethyl-diphenyl ether,bis-(4-hydroxy-3-isobutylphenyl)ether,bis-(4-hydroxy-3-isopropylphenyl)ether,bis-(4-hydroxy-3-chlorophenyl)ether, bis-(4-hydroxy-3-fluorophenyl)ether, bis-(4-hydroxy-3-bromophenyl)ether, bis-(4-hydroxynaphthyl)ether,bis-(4-hydroxy-3-chloronaphthyl) ether, bis-(2-hydroxydiphenyl)ether,4,4'-dihydroxy-2,6-dimethoxydiphenyl ether, and4,4'-dihydroxy-2,5-diethoxydiphenyl ether.

The preferred dihydric polynuclear phenols are represented by theformula: ##STR10## wherein A and A₁ are as previously defined, x and yhave values from 0 to 4 inclusive and R₆ is a divalent saturatedaliphatic hydrocarbon radical, particularly alkylene and alkylideneradicals having from 1 to 3 carbon atoms, and cycloalkylene radicalshaving up to and including 10 carbon atoms. The most preferred dihydricphenol is bisphenol A, i.e., 2,2'-bis(p-hydroxyphenyl)propane.

As condensing agents, any aldehyde may be used which will condense withthe particular phenol being used, including formaldehyde, acetaldehyde,propionaldehyde, butyraldehyde, heptaldehyde,, cyclohexanone, methylcyclohexanone, cyclopentanone, benzaldehyde, and nuclearalkyl-substituted benzaldehydes, such as toluic aldehyde,naphthaldehyde, furfuraldehyde, glyoxal, acrolein, or compounds capableof engendering aldehydes such as para-formaldehyde, hexamethylenetetramine. The aldehydes can also be used in the form of a solution,such as the commercially available formalin. The preferred aldehyde isformaldehyde.

The halo-epoxy alkane can be represented by the formula: ##STR11##wherein X is a halogen atom (e.g., chlorine, bromine, and the like), pis an integer from 1-8, each R₂ individually is hydrogen or alkyl groupof up to 7 carbon atoms; wherein the number of carbon atoms in any epoxyalkyl group totals no more than 10 carbon atoms.

While glycidyl ethers, such as derived from epichlorohydrin, areparticularly preferred in the practice of this invention, the epoxypolymers containing epoxyalkoxy groups of a greater number of carbonatoms are also suitable. These are prepared by substituting forepichlorohydrin such representative corresponding chlorides or bromidesof monohydroxy epoxyalkanes as 1-chloro-2,3-epoxybutane,1-chloro-3,4-epoxybutane, 2-chloro-3,4-epoxybutane,1-chloro-2-methyl-2,3-epoxypropane, 1-bromo-2,3-epoxypentane,2-chloromethyl-1,2-epoxybutane, 1-bromo-4-methyl-3,4-epoxypentane,1-bromo-4-ethyl-2,3-epoxypentane, 4-chloro-2-methyl-2,3-epoxypentane,1-chloro-2,3-epoxyoctane, 1-chloro-2-methyl-2,3-epoxyoctane, or1-chloro-2,3-epoxydecane.

Although it is possible to use haloepoxyalkanes having a greater numberof carbon atoms than indicated above, there is generally no advantage inusing those having a total of more than 10 carbon atoms.

Some commercially available epoxy resins include Dow Tactix 742, ShellRSL-1107, Epon 828, Epon 1031, Hi-Tek Polymers Epi-Rez SU-8 and SU-6,Ciba-Geigy Araldite LT 8011, LT8052, LT 8049, LT 8047, CY 8043 and CY179.

Epi-Rez SU-8 is represented by the following formula: ##STR12##

Dow Tactix 742 is represented by the formula: ##STR13##

Shell Epon 1031 is represented by the formula: ##STR14##

Epoxy polymers containing triazine containing groups are described inU.S. Pat. No. 4,489,202, disclosure of which is incorporated herein byreference.

In addition, the polyepoxides of halo epoxy alkane of the type discussedabove and a polynuclear dihydric phenol of the type above can beemployed. The preferred polyepoxides of this class being thepolyepoxides of epichlorohydrin and bisphenol A (i.e.,2,2-bis(p-hydroxyphenyl)propane.

Examples of representative maleimides are commercially available and canbe represented by the following structural formula: ##STR15## wherein Ris a difunctional alkylene radical such as --CH₂)_(n) and/or as divalentarylene groups such as ##STR16##

A preferred bismaleimide employed is methylene dianiline bismaleimide,represented by the formula: ##STR17##

When a maleimide resin is employed, it is desirable to employ aheat-sensitive free radical initiator in order to facilitate the curing.Suitable free radical initiators include peroxides such as dicumylperoxide and t-butyl perbenzoic peroxide; and azobisisobutyronitrile.When employed, the free radical initiator is present in amounts up toabout 0.5% by weight and preferably about 0.005% to about 0.2% by weightbased upon the amount of maleimide resin in the composition.

Commercial biscyanate/bismaleimide mixtures are known as BT resins. Theyare available from Mitsubishi Gas Chemical Co., Inc., Japan.

The organic modifiers, when employed, can be present in amounts of up toabout 80% and preferably up to about 60% by weight based upon the totalsolids content of the composition.

The compositions of the present invention can also include inorganicfillers such as fumed silica, quartz, glass, ceramics, beta-eucryptite,beta-spodumene, solgel ceramics and micro-balloons. The inorganicfilters can be present in amounts of up to about 75% by weight andpreferably about 20% to about 60% by weight based upon the total solidscontent of the composition.

In addition, the compositions, when desired, can include an organicnon-reactive diluent to facilitate the coating operation. Examples ofsuitable solvents include ketones such as methyl ethyl ketone, methylisobutyl ketone and methyl amyl ketone, and methylene chloride. Whenemployed, the diluent is present in an amount sufficient to providecompositions for coating application.

The compositions can be coated onto substrates such as metal, compositessuch as epoxy, cyanate ester, and polyimide based laminates, ceramics,and glass or other materials onto which photoprocessable coatings arenormally employed. The compositions can be applied by various knowncoating techniques such as spinning, spraying, dipping, film laminatingor passing the substrate through a bath of the composition.

The compositions after coating onto a substrate and removal of volatilesolvents, if present, the coating is imagewise exposed to actinic lightand preferably to ultraviolet light radiation in a predetermined patternwith energy ranging from 0.1-5 Joules/cm². The exposure being through animage-bearing transparency of the desired pattern.

The cyanate ester composition is then subjected to elevated temperaturesof about 45° C. to about 150° C. and preferably about 70° C. to about120° C. This heating is usually carried out for about 5 to about 60minutes and preferably about 10 to about 45 minutes.

In the case of those compositions acting as negative workingphotosensitive compositions (those containing a cationic initiator thatyields a Lewis acid), the exposure and subsequent heating results inpolymerization of those areas of the composition subjected to theactinic light. On the other hand, in the case of those compositionsacting as positive working photosensitive (those containing a cationicinitiator that yields a Bransted acid), the areas subjected to theactinic light are retarded from polymerizing upon subsequent heating.

After exposure to actinic light and subsequent heating, the coating isdeveloped by removing areas not struck by actinic light in the case ofnegative resist or by removing areas struck by actinic light in the caseof positive resist. This can be accomplished by immersing or sprayingthe film with a suitable solvent. Some suitable solvents include ketonessuch as methyl ethyl ketone and methyl isobutyl ketone; methylcarbitolbutylcarbitol, methyl chloroform, α-butyrolactone and methyl amylketone. The solvent selected is one which will dissolve the uncuredcyanate ester composition without attacking, to any undesired extent,the cured composition. Suitable solvents can be readily determined bypersons skilled in the art once they are aware of the present disclosurewithout undue experimentation.

Moreover, when desired, the film can be post-cured by subjecting thefilms to elevated temperatures such as about 85° C. to about 360° C. andpreferably about 150° C. to about 300° C. for about 20 to about 180minutes.

The negative working photosensitive compositions can also be used assolder mask, permanent resist and imageable dielectric material for usein a multilayer circuit structure.

The following non-limiting examples serve to illustrate preferredembodiments of the present invention and are not intended to limit theteachings as set forth herein.

EXAMPLE 1

A stock cyanate ester composition is prepared by mixing about 100 partsby weight of a 75% solids solution of 2,2-bis(p-cyanatophenyl)-propane)prepolymer in methyl ethyl ketone (available under the trade designationAro Cy B - 40S from Hi-Tek Polymers, Inc., Louisville, Ken.), about 33parts by weight of methyl ethyl ketone, and about 0.2 parts by weight ofsolution of zinc octoate (8% zinc) in mineral spirits (available underthe trade designation Hex-Cem from Mooney Chemicals Inc., Cleveland,Ohio). To about 10 parts by weight of the above stock cyanate estercomposition are added about 0.3 grams of RD-87-356 photoinitiator fromCiba-Geigy.

A 14 micron dry film is formed by coating the solution by means of a No.20 wire rod onto an epoxy-fiberglass laminate coupon, followed by dryingat 100° C. for 5 minutes in a forced air oven. The resist film is thenexposed to about 1.5 Joules/cm² of U.V. light under a exposed to about1.5 Joules/cm² of U.V. light under a glass mask, followed by baking atabout 100° C. for about 10 minutes. After being developed in a beakercontaining methyl isobutyl ketone, the coupon is heated at about 177° C.for about 30 minutes to achieve further curing. This formulationprovides a negative working resist.

EXAMPLE 2

A cyanate ester photosensitive composition is prepared by mixing about40 parts by weight of a 75% solids solution of2,2-bis(p-cyanatophenyl)-propane) in methyl ethyl ketone (availableunder the trade designation Aro Cy B-40S from Hi-Tek Polymers, Inc.,Louisville, Ky.), about 0.6 parts by weight of a solution of zincoctoate (8% zinc) in mineral spirits (available under the tradedesignation Hex-Cem from Mooney Chemicals Inc., Cleveland, Ohio), andabout 1.5 parts by weight of RD-87-356 photoinitiator from Ciba-Geigy.

After mixing, the above solution is coated by means of a wire rod on apiece of 10 mil thick copper and dried in a forced air convection ovenfor about 15 minutes at about 60° C. The thickness of a dried film isabout 1 mil. This sample is exposed through a Stauffer Graphic Arts stepwedge and line resolution pattern to 954 mJ/cm² of U.V. light. Then thesample is baked in an oven at about 100° C. for about 30 minutes,followed by a development in a solution of butyl carbitol/MIBK (75%/25%)for about 2 minutes. The sample is heated at about 250° C. for 30minutes to achieve further curing. The resultant relief image shows step5 retained and very good resolution, 1 mil line and 1 mil spaces. Thisformulation provides a negative working resist.

EXAMPLE 3

A photosensitive composition is prepared by admixing about 50 parts ofmethyl ethyl ketone, about 20 parts of bismaleimide/cyanic acid ester(available under the trade designation BT-2170 from Mitsubishi GasChemical, Inc.), about 15 parts of Araldite LT-8011 epoxy available fromCiba-Geigy, about 15 parts of CY-179 epoxy, and about 5 parts ofphotoinitiator GEUVE-1014M. The composition is coated onto anepoxy-glass laminate and then dried to remove the methyl ethyl ketone.The sample is then placed under a glass mask and exposed to 2 Joules/cm²of ultraviolet light. After exposure, the sample is heated in a forcedair oven at about 130° C.-155° C. for about 11 minutes. A photoimage isobtained by developing in methyl ethyl ketone with the composition isthe exposed area being washed away. The sample is heated at 300° F. forabout 30 minutes to complete the curing of the coating.

EXAMPLE 4

Example 3 is repeated, except that composition contains about 3 parts byweight of Araldite LT 8011, about 7 parts by weight of BT-2170, andabout 5 parts by weight of GEUVE-1014M. The composition acts as apositive resist.

Having thus described our invention, what we claim as new and desire tosecure by Letters Patent is:
 1. A method for the production of a resistimage which comprises:providing on a substrate a positive photosensitivecomposition containing a cationically curable cyanate ester orprepolymer thereof and a cationic photoinitiator, wherein said cationicphotoinitiator is a cationic initiator that generates a Bronsted acidupon exposure to actinic light and is present in an amount sufficient toretard polymerization of said cyanate ester or prepolymer thereof,imagewise exposing said composition in a predetermined pattern toactinic light; then heating said composition; and then developing byremoving those portions of said composition that were exposed to saidactinic light to thereby provide said resist image.
 2. The method ofclaim 1 wherein said photoinitiator is an onium salt of a Group VIA or aGroup VIIA element.
 3. The method of claim 1 wherein said photoinitiatoris a sulfonium salt.
 4. The method of claim 1 wherein saidphotoinitiator is present in an amount of about 0.5% to about 10% byweight based upon the solids weight of the composition.
 5. The method ofclaim 1 wherein said photoinitiator is present in an amount of about 3%to about 5% by weight based upon the solids weight of the composition.6. The method of claim 1 wherein said cyanate ester is represented bythose materials containing the following group: ##STR18## wherein Arepresents independently a simple bond, S, S--S, SO, SO₂, CO, CO₂, O,C(CF₃)₂, divalent alkylene radical, divalent alkylene radicalsubstituted with heteroatom, divalent alkylene radical interrupted byheteroatom in the chain, divalent cyclic alkylene group, or divalentarylene group, and each R is independently selected from the groupconsisting of hydrogen, alkyl containing 1-9 carbon atoms, arylcontaining 6-14 carbon atoms, alkaryl containing 6-14 carbon atoms, andhalogen, and each n independently is an integer of from 0-4.
 7. Themethod of claim 1 wherein said cyanate ester is a prepolymer.
 8. Themethod of claim 1 wherein said composition further includes aphotosensitizer.
 9. The method of claim 1 wherein said compositionfurther includes an organic monomer or organic polymer, or both.
 10. Themethod of claim 9 wherein said organic polymer is an epoxy polymer. 11.The method of claim 9 wherein said organic monomer is a maleimide. 12.The method of claim 11 wherein said maleimide is represented by thefollowing formula: ##STR19## wherein R is a divalent alkylene radical ora divalent arylene group.
 13. The method of claim 12 wherein saidmaleimide is methylene dianiline bismaleimide.
 14. The method of claim 1wherein said composition further includes an inorganic filler.
 15. Themethod of claim 1 wherein said cyanate ester is selected from the groupof 2,2-bis(p-cyanatophenyl)-propane, 2,2-bis(p-cyanatophenyl) hexafluoropropane, and prepolymers thereof.
 16. The method of claim 1wherein said cyanate ester is a polyaromatic cyanate ester containingcycloaliphatic bridging group between aromatic rings.
 17. The method ofclaim 1 which further includes subjecting said composition to elevatedtemperatures of about 45° C. to about 150° C. after the imagewiseexposing and prior to the developing.
 18. The method of claim 17 whichfurther includes subjecting the composition to temperatures of about 85°C. to about 360° C. after the developing.
 19. The method of claim 1wherein said actinic light is ultraviolet light.